Notes:

• The ->do( ) is called ->dbh_do( ) as PHP sees 'do' as a reserved word even though it is a class function definition.
• Not every function in the perl DBI/DBH is supported.
• To get errors on prepared statements, you have to check $sth->errstr and NOT $dbh->errstr (see the code below).
• You can not make twp DBI objects that connect to two different databases if they share the driver, host, user, and password (at least for MySQL). This is because PHP reuses database connections if it sees all of the above match a previous connection. What ends up happening is the last DBI object becomes the selected database for all DBI objects that share the said parameters. To get around this, you have to change something in the connection, e.g. the user name. class.DBI will warn you if you try to do this.
• To install this, put the class.DBI and class.DBD::* files somewhere in your php include path.

Example Code and Some Embedded Documentation

require( 'class.DBI' );
//Get a new dbh. Note the way that we check to see 
//  if the connection was made or not.  This is 
//  because as far as I can tell, the "New" 
//  constructor cannot return anything but '$this', 
//  e.g. 'undef'.  Change the 'dbi:...' to 'pdbi:...' for 
//  persistent connections.
$dbh = new DBI( 'dbi:mysql:database;mysql_host', 'user', 'secret' );
if( ! $dbh->dbh ){
  echo "Could not connect to the database.<br>\n";
  exit( );
}

//If you want to use Informix, be sure to setenv the two variables.
setenv( "INFORMIXDIR=/path/to/informix" );
setenv( "INFORMIXSERVER=defaultserver" );
$ifx_dbh = new DBI( 'dbi:Informix:database@hostalias', 'user', 'secret' );


$sth = $dbh->prepare( 'SELECT COUNT(*) FROM some_table' );
if( $sth ){ 
  $sth->execute( ); 
  echo "sth executed.<br>\n";
  $row = $sth->fetchrow_array( );
  echo "Row: ".$row[0]."<br>\n";
  $sth->finish( );
} else {
  echo "Could not prepare query.<br>\n";
}


//Get data by column name.

$sth = $dbh->prepare( 'SELECT * FROM some_table' );
if( $sth ){ 
  $sth->execute( ); 
  while( $row = $sth->fetchrow_hash( )){
    echo "Data: ".$row[column_name]."<br>\n";
  }
  $sth->finish( );
} else {
  echo "Could not prepare query: ".$sth->errstr."<br>\n";
}

//Insert some data...
$query = "INSERT INTO some_table VALUES( '1', 'some text' )";
$count = $dbh->dbh_do( $query );
if( $count ){
  echo "Inserted $count row.<br>\n";
} else {
  echo "Insert Failed: ".$dbh->errstr."<br>\n";
}

//Get the insert ID (assuming you have a serial column):
$serial = $dbh->insert_id( );


//Disconnect from the database.  Do not call
//  this if you are going for persistent connections or
//  you connection will no longer be persistent.
$dbh->disconnect( );